This invention relates to a semiconductor device for use mainly in an optical communication field and in particular to a semiconductor optical device.
It is known in an optical communication technique to connect an optical fiber between a transmitter and a receiver for communication. A light emitting element is used as the transmitter and a light detecting element as the receiver. For a communication to be effected between the transmitter and the receiver both the light emitting element and light detection element are required both at the transmitter side and at the receiver side. A semiconductor device as shown, for example, in FIG. 1 can be used as such light emitting and detecting elements. In actual practice, however, such a device has encountered inconveniences in its use as both a light emitting element and a light detecting element. Furthermore, it would be impossible to reduce the number of parts required. Such a semiconductor device is called "Burrus" type light emitting element and manufactured as follows:
An n-conductivity type Ga.sub.0.7 Al.sub.0.3 As layer 2, p-conductivity type GaAs layer 3, p-conductivity type Ga.sub.0.7 Al.sub.0.3 As layer 4 and p-conductivity type GaAs layer 5 are formed by a liquid phase growth method on one surface of an n-conductivity type GaAs substrate 1 so as to be superposed in that order as shown in FIG. 1. An SiO.sub.2 film 6 is formed on the GaAs layer 5 and its central portion is opened to permit a corresponding surface portion of the GaAs layer 5 to be exposed. An electrode 7 is formed on the SiO.sub.2 film 6 in a manner to fill up the opening of the SiO.sub.2 layer 6 for electrical connection to the GaAs layer 5. An opening is formed in the central area of the other surface of the substrate 1 and one end of an optical fiber 8 extends into the opening of the substrate 1. An electrode 9 is formed on the other surface of the substrate 1.
When a voltage is applied between the electrodes 7 and 9, a light is emitted from a region 3a in the p-conductivity type layer 3 (an activated layer), which is located above the opening of the insulating layer 6. The emitted light enters into the optical fiber 8 through the opening of the substrate 1. In this way, the device functions as a light emitting device. When, on the other hand, a light is sent through the optical fiber 8 toward the device, it reaches a pn junction between the layers 2 and 3 to develop a photoelectromotive force at the pn junction. If a resistor is connected between both electrodes 7 and 9, then an output corresponding to an amount of incident light can be taken off. As evident from this explanation the device uses the same potential when it is used as both the light emitter and light detector. For the device to be used as both the light emitter and light detector, it is necessary at the external circuit of the device to effect insertion of a resistor as well as separation of a light emission operation circuit. In consequence, a bulkier and complicated device results.